Blood treatment apparatuses with a blood treatment unit through which a patient's blood flows are generally known. These include, for example, the known hemodialysis, hemofiltration or hemodiafiltration apparatuses. The known blood treatment apparatuses can be operated in the single-needle or double-needle operation.
With the double-needle technique, the blood is drawn off from the patient's blood vessel via a first needle, conveyed into the blood treatment unit of the blood treatment apparatus and returned into the patient's blood vessel via a second needle. For the removal and return of the blood, use is made of exchangeable hose systems with a blood supply line and blood return line, to which the two needles are connected. The hose systems, which are to be thrown away, are also referred to as disposables.
With the single-needle technique, the removal and return of the blood takes place via a single needle. The blood removed from the patient is stored in a reservoir during an arterial phase, in order then to be returned in a venous phase from the storage unit into the patient's blood system through the same needle.
A blood treatment apparatus for the single-needle operation is known from EP-A-0 472 480 B1. In an embodiment of the known blood treatment apparatus, two blood expansion chambers are provided for temporary storage of blood, which are disposed upstream and downstream of the blood treatment unit. The blood treatment apparatus has a control device, which keeps the pressure in the expansion chambers essentially constant. Level sensors are provided in order to detect the level of the liquid in the expansion chambers.
DE 10 2005 001 779 A1 describes a set for a disposable for the operation of a blood treatment apparatus in the single-needle or double-needle operation. Apart from the blood supply line and blood return line for the connection to the blood treatment unit, the disposable comprises an expansion unit which can be coupled to the air separation unit in order to increase the volume for the single-needle operation. During the single-needle operation, blood is conveyed through the blood supply line into the blood treatment unit and out of the blood treatment unit into the air separation and expansion unit in the arterial phase, the blood supply to the patient being interrupted. A predetermined pressure is built up in the air separation and expansion unit, which is monitored by means of a pressure measuring unit. By means of a compressed air unit, a predetermined pressure can be established in the expansion and air separation unit by actuating an air pump which is incorporated between a tank and the expansion unit. Moreover, it is proposed to calculate the blood volume in the expansion and air separation unit with the aid of the measured values from three pressure sensors and the known system volumes. Furthermore, it is proposed to use the air pump to regulate the pressure in the venous phase, so that the delivery rate of the blood can be adapted in the optimum fashion.
An object of the present invention is to provide a device for blood treatment for the single-needle operation, wherein the blood volume in the blood reservoir can be ascertained without level sensors and the behavior in the case of malfunction can be improved. Moreover, it is an object of the present invention to provide a blood treatment method in the single-needle operation, wherein the blood volume in the blood reservoir can be ascertained without level sensors and the behavior in the case of malfunction can be improved.